Using 5.0ghz Antennas with 2.4ghz Access Point.

[Erfan Mojaddam]

I'm working in a campus environment that has an existing wireless network using a Cisco AIR-WLC2112-K9 controller.

There are 8 AIR-LAP1242G-A-K9 access points connected to the  controller. Each access point has a 5.0GHZ 4.5dbi Cisco omnidirectional  antenna, although the AP only supports 2.4GHZ.

Q1. Can anyone help me understand why a 5.0ghz antenna  might had been used with a 2.4ghz AP, and if we can expect increased  performance if we replace the antennas with 2.4ghz ones?

Q2.  On the controller, the antenna gain is set to 0 for each AP. Is there  also a benefit to leaving that 0 as opposed to 9 for 4.5dbi?

Thanks for any tips/advice.

[Scott Fella]

I the antenna is specifically for the 5ghz, it will not work on the 2.4ghz. You need to make sure you replace those with 2.4ghz antennas. The gain is really a reference and I really don't change that unless I have WCS/NCS.

Thanks,

Scott Fella

Sent from my iPhone

[grabonlee]

The 5ghz antenna is tuned to handle frequencies in the 5ghz range. Using them on 2.4ghz APs, does not mean that the AP will not still radiate signals from its internal radiator (IR). However, as the antenna will filter out the 2.4ghz frequency, there will be no gain added to the signal, hence the EIRP will be much lower due to considerable loss.

[Leo Laohoo]

There are 8 AIR-LAP1242G-A-K9 access points connected to the  controller. Each access point has a 5.0GHZ 4.5dbi Cisco omnidirectional  antenna, although the AP only supports 2.4GHZ.

That's not correct.  You WAP is a 1242.  This means that this model has TWO (2) wifi radios, 2.4 Ghz and 5.0 Ghz.

Q1. Can anyone help me understand why a 5.0ghz antenna  might had been used with a 2.4ghz AP, and if we can expect increased  performance if we replace the antennas with 2.4ghz ones?

Someone used 5.0 Ghz antennas into 2.4 Ghz radio maybe out of ignorance?  Sticking the wrong antenna means the the radio signal won't propagate.

Q2.  On the controller, the antenna gain is set to 0 for each AP. Is there  also a benefit to leaving that 0 as opposed to 9 for 4.5dbi?

Not really.  If you have a 4.5 dBi antenna, then you can put the value of 9.

[Erfan Mojaddam]

Thanks everyone. I'll try out 2.4ghz antennas and test the signal.

Leolaohoo, the AIR-LAP1242G-A-K9 model only has 2.4ghz radios. It's the AIR-LAP1242AG-A-K9 model that has both the 2.4 and 5.0ghz radios.

[Leo Laohoo]

Leolaohoo, the AIR-LAP1242G-A-K9 model only has 2.4ghz radios. It's the AIR-LAP1242AG-A-K9 model that has both the 2.4 and 5.0ghz radios.

Yup.  That's correct.  I was mistaken.